Update katex to latest version (go-gitea#33361)

Partial backport of go-gitea#33359.
Upgrade katex because there were a number of security problems fixed in
recent versions.

Author: silverwind

package-lock.json

@@ -32,7 +32,7 @@
     "htmx.org": "2.0.4",
     "idiomorph": "0.3.0",
     "jquery": "3.7.1",
-    "katex": "0.16.11",
+    "katex": "0.16.21",
     "license-checker-webpack-plugin": "0.2.1",
     "mermaid": "11.4.1",
     "mini-css-extract-plugin": "2.9.2",